This invention relates to measuring instruments and more particularly to measuring instruments adapted to measure internal dimensions to a high degree of accuracy.
Various instruments are presently available for the determination of internal dimensions. Such instruments include: inside calipers; inside hand micrometers; master gage plugs; air gage plugs; and electronic internal comparators. The calipers and micrometers, while being exceedingly convenient, are not inherently capable of furnishing readings to a high level of accuracy. Master gage plugs (go and no-go) do not yield a direct measurement and their reliability is to a large extent dependent upon the skill and experience of a user. Air gage plug measurements, which are very accurate, mandate the provision of a separate air gage plug and gaging master (since it is a comparative type instrument) for each size being measured. The electronic internal comparator is extremely accurate but must be set-up for each size being measured. While this latter-mentioned instrument is well-suited for master gage rings, it is not readily usable for random measurements of precision parts. In addition, such electronic internal comparators do not have the capability of measuring internal pitch diameters.